The invention disclosed herein relates generally to optical instruments and methods. Stated more particularly, disclosed and protected by the present patent is a scanning confocal device for scanning an object with an optical beam, detecting the light remitted from or reflected by the object, and generating an image of the object.
Confocal imaging techniques include the illumination of objects with a xe2x80x9cflying spotxe2x80x9d and the detection of light that is reflected from or otherwise remitted by the currently illuminated point on the object located only in the image plane. This provides better spatial resolution, better contrast to the image, and less depth of field than conventional optical devices. The small depth of field allows for the creation of 3-D images of semi-transparent objects. Scanning imaging techniques are employed in confocal laser scanning microscopes (CLSM), tandem scanning microscopes (TSM), scanning laser ophthalmoscopes (SLO), and other applications.
A TSM is discussed in Petran et al., xe2x80x9cTandem-Scanning Reflected-Light Microscope,xe2x80x9d Journal of the Optical Society of America 1968 Vol. 58, No. 5, pp 661-664. Petran et al. acknowledged that reflected-light microscopy of semi-transparent material is usually unsatisfactory because of low contrast and light scattering. They describe the TSM, in which both the object plane and the image plane are scanned in tandem. In the Petran et al. system, the object is illuminated with light passing through holes in one sector or side of a rotating scanning disk, known as a Nipkow disk. The scanning disk is imaged by the objective at the object plane. Reflected-light images of these spots thereby produced are directed to the diametrically opposite side of the same disk. With this, light can pass from the source to the object plane, and, from the object plane to the image plane, only through optically congruent holes on diametrically opposite sides of the rotating disk.
Tandem scanning confocal arrangements, however, are xe2x80x9clight-starvedxe2x80x9d by the limited brightness of the illumination spot. TSM systems, in addition, are hampered by stray light scattered from the moving pinhole array.
Current flying spot systems benefit from the advent of the laser. They use moving optical elements for deflecting a laser beam, so that an illumination spot is swept across the object to be scanned.
A recent version of a CLSM is described in U.S. Pat. No. 5,532,873 of Dixon. The scanning of the laser beam is provided by two mirrors, rotationally oscillating around axes that are perpendicular to each other.
A confocal scanning laser ophthalmoscope (CSLO) is disclosed in Webb et al, xe2x80x9cConfocal Scanning Laser Ophthalmoscope,xe2x80x9d Applied Optics, Vol. 26, No. 8, Apr. 15, 1987, pp 1492-1499. The apparatus uses multiple scanning elements, including a multifaceted rotating polygonal reflector scanner, to provide scanning of both incident and reflected light at television-rate frequencies. The CSLO scans an illumination spot over the fundus of an eye, and synchronously scans a detector over the image.
Other confocal devices, are discussed in The Handbook of Biological Confocal Microscopy, 2nd edition. Pawley, ed., Plenum Press, 1995.
Conventional scanning devices of the type discussed require a multiplicity of mechanical components moving at high speed. They are typically bulky and require significant power to drive the scanning mechanism.
A confocal scanning device without moving parts is described in U.S. Pat. No. 5,028,802 of Webb et al,. FIG. 1A of the present application (which is FIG. 1C of the ""802 patent) provides a summary of the Webb et al. invention and is prior art. FIG. 1B of the present application (FIG. 3 of the ""802 patent) shows the preferred embodiment of the ""802 patent.
Referring to FIG. 1C of the ""802 patent (FIG. 1A of the present application), the scanning arrangement employs Nxc3x97M array 10 of microlasers in a scanning mode as the illumination source. As shown in FIG. 1A of the present application (FIG. 1C of Webb), the device includes a laser scan drive 16 for energizing the lasers of array 10. The microlasers are energized sequentially, so that the array 10 is scanned in a conventional TV raster fashion. The array 10 is imaged on the object 18 to be illuminated thereby providing raster illumination of the object 18. Light 19 emitted from the object, by reflection, scatter or transmission, is then detected by detector 20 and the detection signal, carried on line 21, is displayed synchronously with the array scan, to provide a video image on a monitor or other image output device 22 driven by SYNCH signals provided by drive 16 on line 24.
Referring to FIG. 1B of the present application (FIG. 3 of Webb), a confocal scanning configuration uses a detector array having independently addressable photodiodes, that are optically congruent to microlasers. Lens L directs light from scanned source array 10 onto the object plane OB, and light reflected from the object is directed to detector 20 by beam splitter S. A lens Lxe2x80x2 is used to direct light reflected from the object onto discrete photodiodes of a detector array 20xe2x80x2. These photodiodes are read individually, in a pattern that is, and are synchronized with the scanning-illumination of the object. Thus, light scattered from non-illuminated portions of the object does not contribute to the output of the detection device, unless it impinges upon the selected portion of the detector. As a result, noise due to unwanted scattered light is significantly reduced.
U.S. Pat. No. 5,034,613 to Denk et al., which issued Jul. 23, 1991 for Two-Photon Laser Microscopy, discloses a laser scanning microscope in which fluorescent light is detected in a manner intended to avoid photo-bleaching.
U.S. Pat. No. 5,071,246 to Blaha et al., which issued Dec. 10, 1991 for Confocal Scanning Ophthalmoscope, discloses the use of light wave conductors.
U.S. Pat. No. 5,120,953 to Harris, which issued Jun. 9, 1992 for Scanning Confocal Microscope Including A Single Fiber For Transmitting Light To and Receiving Light From An Object, discloses the use of optical fibers for transmitting light and a light separator to divert the return light to a detector.
U.S. Pat. No. 5,296,703 to Tsien, which issued Mar. 22, 1994 for Scanning Confocal Microscope Using Fluorescence Detection, discloses the use of a beam of radiation and detection of the resulting fluorescence using beam splitters and rotatable scanning mirrors and a raster scan display.
U.S. Pat. No. 5,325,386 to Jewell et al., which issued Jun. 28, 1994 for Vertical-Cavity Surface Emitting Laser Array Display System, discloses the use of vertical cavity surface emitting lasers in an array to enhance a display.
U.S. Pat. No. 5,386,112 to Dixon, which issued Jan. 31, 1995 for Apparatus and Method for Transmitted-Light and Reflected-Light Imaging, discloses a microscope using a series of beam splitters and mirrors and light that is reflected is separated from light that is transmitted.
U.S. Pat. No. 5,430,509 to Kobayashi, which issued Jul. 4, 1995 for Scanning Laser Ophthalmoscope, discloses the use of beam splitters and mirrors and uses at least three scanning systems.
U.S. Pat. No. 5,450,501 to Smid issued Sep. 12, 1995 and is directed to an Apparatus for the Point-by-Point Scanning of an Object using frequency selective filtration to operate a system having transmission of light through the object being viewed.
U.S. Pat. No. 5,512,749 to Iddan et al., which issued Apr. 30, 1996 for Infrared Microscope, discloses the use of a cryogenic detection device and an IR array of detectors including a scanning mirror for scanning the object.
U.S. Pat. No. 5,524,479 to Harp et al. issued Jun. 11, 1996 and is directed to a Detecting System for Scanning Microscopes. The patent discloses the use of a cantilevered arm as a probe to examine the object to be viewed.
U.S. Pat. No. 5,563,710 to Webb, which issued Oct. 8, 1996 for Imaging System With Confocally Self-Detecting Laser, discloses using an array of lasers and a single detector. Also, light reflected from the object effects the lasers, which then forward the light to the detector.
U.S. Pat. No. 5,568,463 to Sahara et al. issued Oct. 22, 1996 and discloses a Semiconductor Laser Device To detect A Divided Reflected Light Beam. The patent describes an optical device for detecting a magneto-optical signal in which a light-emitting portion and a light receiving portion are closely disposed on a common substrate.
A general object of the present invention is to provide improved confocal imaging methods and apparatus without the use of moving parts.
A further object of the present invention is to provide such methods and apparatus affording high spatial resolution and enhanced brightness of the image.
Another object of the present invention is to provide such imaging methods and apparatus that is capable of being implemented in a compact and reliable embodiment.
A further object of the present invention is to provide a confocal scanning device that is arranged so that multiple areas of a target may be scanned simultaneously.
Another object of the present invention is to provide a small angle beam splitter (SABS) in a confocal arrangement that permits extremely small angle shifts for light beams.
A further object of the present invention is to provide a device of the type described that is arranged to be used as a microscope.
An additional object of the present invention is to provide a device of the type described that is arranged to be used as an Ophthalmoscope.
A yet further object of the present invention is to provide a confocal device and method that can be accomplished using light fiber bundles, both of the coherent and the non-coherent type.
Still another object of the present invention is to provide for the imaging of an object in fluorescent light.
Yet another object of the present invention is to provide a two-photon confocal device that is versatile and compact.
A further object of the present invention is to provide for complete utilization of light emitted by microlasers thereby to increase the brightness of the image.
These and still further objects and advantages of the present invention will be obvious both to one who reviews the present description and the accompanying drawings and to one who has an opportunity to take advantage of an embodiment of the present invention for an optical confocal device.
In furtherance of these objects, one embodiment of the invention includes a combined array of independently excitable light sources and independently readable detectors that are supplemented by optical elements for directing the light generated by the light sources of the array onto the object and for directing light that is reflected, fluoresced or scattered from the object onto the detectors of the array. There may be rows of light sources and detectors that are interleaved in a combined array. The source/detector array and optical elements can be, and preferably are, stationary relative to one another and relative to the object.
A small angle beam splitter is provided to deflect the reflected and remitted light from the object to the detectors. Since the spacing between adjacent microlasers and detectors is quite small, a bilens is used to provide this shift. The requirement imposed upon such a bilens for there to be some difference (e.g., 5xcexc) between the lenses causes such a bilens to be difficult at best to make. Therefore, an optical system is used wherein the requirements imposed on the bilens can be more in the order of one mm rather than 5 xcexcm. If the spacing between adjacent lasers and detectors is in the range of 10-90xcexc, then the difference in the bilens would be in the range of 5-45xcexc since the difference in the bilens is one half of the spacing of laser to detector.
Each embodiment according to the present invention can be used for the imaging of an object in fluorescent light. The fluorescence technique is used both in an ophthalmoscope for the imaging of a blood vessel picture of the retina and in various applications of microscopy, especially when it is desired to obtain a 3-D view of tissue. It provides high sensitivity to the presence of small amounts of fluorescent substances. The laser scanning technique produces excitation in a target material by absorption of photons thereby to provide intrinsic three-dimensional resolution. The confocal technique additionally brings better image contrast and the opportunity for 3-D fluorescent imaging.
The combined laser/detector array can be arranged for the simultaneous excitation of several spaced light sources that are reflected or otherwise returned to the array where they are detected as long as the direct or reflected, refracted or fluoresced light from the different light sources does not adversely influence any of the other simultaneously excited light sources/detectors combinations. This can provide a several-fold increase in the speed of scanning an object with a confocal device.
The foregoing discussion broadly outlines the more important features of the invention to enable a better understanding of the detailed description that follows and to instill a better appreciation of the inventors"" contribution to the art. Before an embodiment of the invention is explained in detail, it must be made clear that the following details of construction, descriptions of geometry, and illustrations of inventive concepts are mere examples of the many possible manifestations of the invention.